Kekulé versus Lewis: When Aromaticity Prevents Electron Pairing and Imposes Polyradical Character

Some conjugated alternant hydrocarbons, of singlet ground state according to Ovchinnikov’s rule, may exhibit strong polyradical character, despite admitting complete pairing of electrons in bond orbitals between adjacent atoms. Typical organizations of this kind are encountered in polycyclic frames supporting two or more extracyclic methylene groups. Lewis bond pairing would require quinonization of six‐membered rings, whereas safeguarding aromaticity proves sufficient to impose ground‐state open‐shell character, that is, the existence of unpaired electrons, providing the number of benzene rings to be quinonized is larger than two. Several examples built as variations around para‐polyphenylene frames are examined through unrestricted DFT (UDFT) calculations, using various methods for spin decontamination of wavefunctions, geometries, and singlet–triplet energy gaps. They all illustrate how it is possible to conceive architectures that can be written with a closed‐shell bond pairing, although they exhibit a large number of unpaired electrons. The same analyses also apply to systems in which quinonization would not kill but only reduce the number of unpaired electrons.     

Organic electrochemical transistors based on PEDOT with different anionic polyelectrolyte dopants

Recent applications of organic electrochemical transistors (OECTs) in bioelectronics motivate the search for new materials with mixed electronic and ionic conductivity. We investigate the characteristics of a series of poly(3,4-ethylenedioxythiophene) (PEDOT)-based materials with a new class of anionic polyelectrolytes used as dopants and stabilizers, replacing the traditionally used poly(styrene sulfonate) (PSS). We show that the backbone of the polyanion plays a major role in determining device performance, while its molecular weight and the counter ion used during PEDOT synthesis play a less important role. We find that transconductance increases with the degree of swelling of the film, consistent with enhanced ion transport. Finally, we identify a polymer that offers performance close to the state-of-the-art. This work highlights the importance of the polyanion phase as a means to control OECT performance. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 147–151     

Towards Magnetic Carbo‐meric Molecular Materials

Numerous studies have underlined the putative diradical character of π‐conjugated molecules that can be described by closed‐shell Lewis structures, for instance, p‐dimethylene p–n phenylenes, or long polyacenes. In the latter compounds, the only way to save the aromaticity of the six‐membered rings is to give up the Lewis electron pairing in the singlet biradical ground state. The present work considers the possibility of doing the same by using the basic C₂ units of carbo‐meric architectures. A series of acyclic and cyclic carbo‐meric architectures is studied by using UB3LYP DFT broken‐symmetry calculations, including spin decontaminations and subsequent geometry optimization of the singlet diradical. The C₂ units are shown to stabilize the singlet biradical by spin delocalization, two of them playing approximately the same role as one radical‐insulating 1,4 phenylene moiety. The results are generalized to the investigation of open‐shell polyradical singlet states of rigid hydrocarbon structures, the symmetry and rigidity of which can assist cooperativity and self spin polarization effect. Several synthesis targets with challenging magnetic/spin properties are suggested in the carbo‐mer series.     

Photolyse Des (Oxo-3)-Butyl-α et β-D-Mannopyranosides

Abstract

(3-Oxo)-butyl mannopyranosides undergo Norrish type II photocyclization giving hydroxyspiroketals of which the structures have been established by NMR spectroscopy and X-ray analysis. The influence of the anomeric and C-2 configurations have been studied and compared to the gluco derivatives. The favored photocyclization of β-mannoside occurs with retention of configuration and that of α-mannoside with inversion of configuration.     

Thermal Decomposition of Organotin Sulfamates: A One Pot Synthesis of Vinyltributyltin Compounds

The preparation of some alkyltributyltin sulfamates is described. Thermal decomposition of these compounds provides a route to vinyltributyltin derivatives.     

Rough surface contact analysis by means of the Finite Element Method and of a new reduced model

This article presents two approaches of a normal frictionless mechanical contact between an elastoplastic material and a rigid plane: a full scale finite element analysis (FEA) and a reduced model. Both of them use a representative surface element (RSE) of an experimentally measured surface roughness. The full scale FEA is performed with the Finite Element code Zset using its parallel solver. It provides the reference for the reduced model. The ingredients of the reduced model are a series of responses that are calibrated by means of FEA on a single asperity and phenomenological rules to account for asperity–asperity interaction. The reduced model is able to predict the load–displacement curve, the real contact area and the free volume between the contacting pair during the compression of a rough surface against a rigid plane. The CPU time is a few seconds for the reduced model, instead of a few days for the full FEA.     

Stereodivergent Synthesis of Piperidine Alkaloids by Ring‐Rearrangement Metathesis/Reductive Lactam Alkylation of Nitroso Diels–Alder Cycloadducts

A general methodology for the stereoselective synthesis of 2‐(2‐hydroxyalkyl)piperidine alkaloids by ring‐rearrangement metathesis of nitroso Diels–Alder cycloadducts is reported. The approach is illustrated by the formal synthesis of porantheridine and the total synthesis of andrachcinidine through a diastereodivergent allylation of an N‐alkoxy bicyclic lactam. The asymmetric synthesis of the latter alkaloid provides new insights into the configurational stability of cycloadducts between chloronitroso reagents and cyclopentadiene.     

Synthese Et Photochimie Des (Oxo-3)Butyl- α Et β -L-Arabinopyranosides

Abstract

(3-Oxo) butyl-l-arabinopyranosides undergo Norrish II type photocyclization giving hydroxyspiroketals with a low stereo-selectivity but with a greater reactivity for α -l-anomers according to stereoelectronic effects for the photolysis of axial anomeric hydrogens.     

Efficient optimization of fully-integrated inductive DC–DC converters comprising tapered inductor layout synthesis and temperature effects

The evolution of computer-aided design tools has extended the capabilities of a designer by pushing the optimality of complex circuits beyond the ad hoc manual implementation. This work presents a framework to co-optimize the circuit and the layout parameters of fully integrated inductive DC–DC converters. The framework comprises expensive optimization that is speeded up by active learning sample selection and evolutionary techniques to acquire an optimal converter. A tapered inductor topology is used to increase the quality of the on-chip inductor and to improve the efficiency of the overall monolithic DC–DC converter. The optimization framework is validated by co-optimizing the design parameters and the tapered inductor layout for a fully-integrated DC–DC boost converter in a 0.13 μm CMOS technology. The power loss in the circuit is reduced with 27 % resulting in a 7 % efficiency improvement, compared to a fully-integrated DC–DC boost converter with a regular inductor topology.